Method for improving thickness uniformity of deposited ozone-TEOS silicate glass layers

ABSTRACT

A method for depositing highly conformal silicate glass layers via chemical vapor deposition through the reaction of TEOS and O 3  is disclosed. The entire method, which can be performed in a single cluster tool and even in a single chamber, begins by placing an in-process semiconductor wafer having multiple surface constituents in a plasma-enhanced chemical vapor deposition chamber. A &#34;clean&#34; silicate glass base layer that is substantially free of carbon particle impurities on an upper surface is then formed on the wafer surface in one of two ways. The first employs plasma-enhanced chemical vapor deposition using TEOS and diatomic oxygen gases as precursors to first deposit a &#34;dirty&#34; silicate glass base layer having carbon particle impurities imbedded on an upper surface. The dirty base layer is then transformed to a clean base layer by subjecting it to a plasma treatment, which involves flowing a mixture of a diamagnetic oxygen-containing oxidant, such as ozone or hydrogen peroxide, and diatomic oxygen gas into the chamber and striking an RF plasma at a power density setting of about 0.25 to 3.0 watts/cm 2  for a period of from 30-300 seconds. It is hypothesized that the plasma treatment burns off the impurities, which are present in the PECVD-deposited base layer and which may be responsible for certain hydrophilic surface effects which repel TEOS molecules. The plasma treatment also creates a high degree of surface uniformity on the PECVD-deposited glass layer. The second way of forming a clean silicate glass base layer involves flowing hydrogen peroxide vapor and at least one gaseous compound selected from the group consisting of silane and disilane into the deposition chamber. Following the formation of the clean base layer, a subsequent glass layer is deposited over the PECVD-deposited glass layer in the same chamber or cluster tool using chemical vapor deposition and TEOS and ozone as precursor compounds.

This is a Continuation of copending application Ser. No. 08/841,908filed on Apr. 17, 1997.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to processes for depositing compounds by means ofchemical vapor deposition and, more particularly, to processes fordepositing silicon dioxide layers using ozone and tetraethylorthosilaneas precursor compounds.

2. Background of the Invention

Doped and undoped silicon dioxides, which are commonly referred to assilicate glasses, are widely used as dielectrics in integrated circuits.Although silicon dioxide possesses a tetrahedral matrix which willimpart a crystalline structure to the material under proper heating andcooling conditions, the silicon dioxides used as dielectrics inintegrated circuits are typically amorphous materials. This applicationuses the term "silicate glass" to refer to silicon dioxides depositedvia chemical vapor deposition (CVD), as the term encompasses materialscontaining not just silicon dioxide, but dopants and other impurities aswell.

Chemical vapor deposition of silicate glasses has become of paramountimportance in the manufacture of contemporary integrated circuits. Forexample, silicate glass doped with both boron and phosphorous is widelyused as an interlevel dielectric and as a getter material for mobilesodium ions.

Chemical vapor deposition (CVD) of silicate glasses by the semiconductorindustry is most commonly accomplished by reacting tetraethylorthosilane(TEOS), silane or disilane with an oxidizer. Silane is typically reactedwith diatomic oxygen (O₂) or nitrous oxide (N₂ O) at a temperature ofabout 400° C. TEOS, on the other hand, is generally reacted with eitherO₂ or ozone (O₃). If a low reaction temperature is desirable, the use ofozone permits a reduction in the reaction temperature to about half thatrequired for O₂. For the sake of brevity, glass layers deposited fromthe reaction of O₃ and TEOS shall be termed "ozone TEOS glasses".Reaction temperature may also be reduced for the TEOS-O₂ reaction bystriking a plasma in the deposition chamber. Glasses deposited via thisplasma-enhanced chemical vapor deposition (PECVD) method shall bereferred to hereinafter as PECVD-TEOS silicate glasses. The plasmagenerates highly reactive oxygen radicals which can react with the TEOSmolecules and provide rapid deposition rates at much reducedtemperatures.

Silane is used for the deposition of silicate glasses when substratetopography is minimal, as the deposited layers are characterized by poorconformality and poor step coverage. Silicate glasses deposited from thereaction of TEOS with O₂ or O₃ are being used with increasing frequencyas interlevel dielectrics because the deposited layers demonstrateremarkable conformality that permits the filling of gaps as narrow as0.25 μm. Unfortunately, the deposition rate of silicate glass formed bythe reaction of TEOS and O₃ is highly surface dependent. A particularlyacute problem arises when the deposition is performed on a surfacehaving topographical features with non-uniform surface characteristics.For example, the deposition rate is very slow on PECVD-TEOS glasslayers, considerably faster on silicon and on aluminum alloys, andfaster still on titanium nitride, which is frequently used as ananti-reflective coating for laser reflow of aluminum alloy layers. Acorrelation seems to exist between the quality and relative depositionrate of ozone TEOS glass layers. For example, ozone TEOS glass layersthat are deposited on PECVD-TEOS glass layers have rough, poroussurfaces and possess high etch rates.

In U.S. Pat. No. 5,271,972 to K. Kwok, et al., it is suggested that thesurface sensitivity of ozone-TEOS glass layers deposited on PECVD-TEOSglass layers may be related to the presence of a hydrophilic surface onthe PECVD TEOS glass layers. A hydrophilic surface on the PECVD TEOSglass layer may be attributable to embedded elemental carbon particleswhich are formed as the TEOS precursor gas is attached by oxygenradicals generated by the plasma. As elemental carbon particles arecharacteristically hydrophilic, they repel TEOS molecules, which arecharacteristically hydrophobic, and interfere with their absorption onthe surface of the deposited layer. Thus, the poor absorption rate ofTEOS molecules on the surface of PECVD TEOS glass results in slowlydeposited, poor-quality films. Experimental evidence indicates thatdeposition rates are low for hydrophilic surfaces and high forhydrophobic surfaces. For example, titanium nitride, being highlyhydrophobic, readily absorbs TEOS molecules on its surface, whichaccelerates the deposition reaction.

Given the surface-dependent variation in deposition rates, it is notuncommon for ozone-TEOS glass layers to build up rapidly around aluminumconductor lines and much more slowly on PECVD glass layers on which theconductor lines are fabricated, thereby forming cavities of tear-dropcross section between adjacent conductor lines. FIG. 1 is across-sectional view which depicts the undesirable result obtained byconventionally depositing an ozone-TEOS layer 11 over aluminum conductorlines 12 which overlie an underlying PECVD TEOS glass layer 13. Prior topatterning, the aluminum conductor lines 12 were covered with a titaniumnitride layer which served as an anti-reflective coating during a laserreflow operation. A titanium nitride layer remnant 14 is present on theupper surface of each conductor line 12. A cavity 15 having ateardrop-shaped cross section has formed between each pair of conductorlines 12. Cavities in an interlevel dielectric layer are problematicprimarily because they can trap moisture when the deposited glass layeris subjected to a planarizing chemical mechanical polishing step duringa subsequent fabrication step. The moisture, if not completely removedprior to the deposition of subsequent layers, can corrode metalconductor lines during normal use and operation of the part, or it maycause an encapsulated integrated circuit device to rupture if the steamgenerated as the device heats up is unable to escape the package.

In U.S. Pat. No. 5,271,972, a technique is disclosed for improving thefilm quality of ozone-TEOS glass layers deposited on PECVD-TEOS glasslayers. The method involves depositing the underlying PECVD-TEOS layerusing high pressure and a high ozone-to-TEOS flow rate. For the lastseveral seconds of the plasma-enhanced deposition process, a stepwisereduction in reactor power is carried out. It is claimed that thistechnique produces an interstitial silicon dioxide layer at the surfaceof the PECVD-TEOS layer which greatly reduces the surface sensitivity ofsubsequently deposited ozone-TEOS oxide layers.

SUMMARY OF THE INVENTION

This invention provides an alternative method for depositing highlyconformal silicate glass layers via chemical vapor deposition throughthe reaction of TEOS and O₃ and for minimizing surface effects ofdifferent materials on the deposition process.

The entire method, which can be performed in a single cluster tool oreven in a single chamber, begins by placing an in-process integratedcircuit having multiple surface constituents in a plasma-enhancedchemical vapor deposition chamber. A "clean" silicate glass base layerthat is substantially free of carbon particle impurities on an uppersurface is then formed on the wafer surface in one of two ways.

The first way of forming the clean base layer employs plasma-enhancedchemical vapor deposition using TEOS and diatomic oxygen gases asprecursors to first deposit a "dirty" silicate glass base layer havingcarbon particle impurities imbedded on the upper surface. Glass layersdeposited via PECVD by the reaction of TEOS and O₂ tend to haveelemental carbon particles embedded therein. As these particles mayimpart hydrophilic surface characteristics to the deposited glass layerwhich may interfere with the subsequent deposition of dense,high-quality ozone-TEOS glass layers, the base glass layer is subjectedto a plasma treatment which involves flowing a mixture of anoxygen-containing diamagnetic oxidant, such as ozone or hydrogenperoxide or a combination of both, and diatomic oxygen gas into thechamber and striking an RF plasma at a power of 50-350 watts for aperiod of from 30-300 seconds. It is hypothesized that the plasmatreatment burns off the carbon particle impurities that are present onthe surface of the dirty silicate glass base layer, thereby reducing thehydrophilic surface characteristics. The plasma treatment also creates ahigh degree of surface uniformity on the PECVD-deposited O₂ -TEOS glasslayer.

The second way of forming the base layer involves flowing hydrogenperoxide vapor and at least one gaseous compound selected from the groupconsisting of silane and disilane into the deposition chamber. As anoptional step, the clean base layer formed via this second method may besubjected to a plasma treatment identical to that performed on the dirtyPECVD-deposited O₂ -TEOS glass layer. This optional plasma treatmentstep is performed merely to improve surface uniformity, not reducehydrophilic surface characteristics.

Following the formation of the clean base layer, a final glass layer isdeposited over the PECVD-deposited glass layer using chemical vapordeposition and TEOS and ozone as precursor compounds.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a portion of an in-processintegrated circuit which has been subjected to a conventional blanketdeposition of ozone-TEOS silicate glass;

FIG. 2 is a cross-sectional view of a portion of an in-processintegrated circuit identical to that of FIG. 1 following deposition of abase glass layer;

FIG. 3 is a cross-sectional view of the in-process circuit portion ofFIG. 2 following plasma treatment;

FIG. 4 is a cross-sectional view of the in-process circuit portion ofFIG. 3 following the deposition of a final ozone-TEOS glass layer; and

FIG. 5 is a flow chart summarizing the various steps of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

This invention is embodied in a process for depositing highly conformalsilicate glass layers via chemical vapor deposition through the reactionof tetraethylorthosilane (TEOS) and O₃. The entire process, which can beperformed in a single cluster tool or even in a single chamber, beginsby placing an in-process semiconductor wafer in a plasma-enhancedchemical vapor deposition chamber. In a typical case, hundreds ofintegrated circuits are undergoing simultaneous fabrication on thewafer, and each integrated circuit has topography with multiple surfaceconstituents. FIG. 2 is a cross-sectional view which depicts a smallportion of an integrated circuit identical to that of FIG. 1. Aplurality of parallel aluminum conductor lines 12 overlies a silicondioxide layer 13. Each aluminum conductor line 12 is covered with atitanium nitride layer 14 which served as an anti-reflective coatingduring a laser reflow operation which preceded masking and etching stepswhich formed the conductor lines. Each of the different materials hasdifferent surface characteristics which affect the rate of depositionfor ozone-TEOS glass layers.

In order to eliminate surface characteristics, a "clean" silicate glassbase layer is formed which completely covers all existing topography.The base layer must be clean in the sense that its upper surface is freeof hydrophilic carbon particle impurities which would interfere with thedeposition of an ozone-TEOS final glass layer. The clean base layer maybe formed in one of two ways.

Referring now to FIG. 2, the first way involves depositing a "dirty"base silicate glass layer 21 on all constituent surfaces viaplasma-enhanced chemical vapor deposition (PECVD). The PECVD depositionof the base silicate glass layer 21 is performed in a deposition chamberin which a plasma is ignited in a plasma formed from a mixture of TEOS,oxygen and an inert carrier gas such as helium or argon which transportsTEOS molecules to the chamber.

Deposition of the PECVD base silicate glass layer 21 is effected withina plasma deposition chamber at a pressure within a range of about 1-50torr (preferably within a range of about 1-10 torr), an oxygen flow rateof about 100-1000 sccm, a carrier gas flow rate of about 100-1500 sccm,and with an RF power density of about 0.7 watts/cm² to about 3.0watt/cm². The deposition temperature is maintained within a range ofabout 300° to 500° C., with a preferred temperature of about 375° C.This process is described in greater detail in U.S. Pat. No. 4,872,947,which issued to Chang, et al., and is assigned to Applied Materials,Inc. This patent is incorporated herein by reference.

A suitable CVD/PECVD reactor in which the present process can be carriedout in its entirety is also described in U.S. Pat. No. 4,872,947.Silicate glass layers can be deposited using standard high frequency RFpower or a mixed frequency RF power.

The base glass layer 21 is deposited to an average thickness within arange of about 100 to 1000 Å. The optimum thickness is deemed to beapproximately 500 Å. Although the deposition rate of plasma-enhancedchemical-vapor-deposited oxide from TEOS and O₂ is more even ondifferent surfaces than it is for ozone-TEOS oxide, it is essential thatall surfaces are completely covered.

An untreated TEOS silicate glass layer deposited via a plasma-enhancedCVD process tends to have embedded elemental carbon particles which areformed as the TEOS precursor gas is attacked by oxygen radicalsgenerated by the plasma. These carbon particles apparently imparthydrophilic surface characteristics to an untreated base silicate glasslayer 21 which are most likely responsible for the uneven depositionrates observed during subsequent depositions of dense, high-qualityPECVD ozone-TEOS glass layers. In order to reduce or eliminate suchinterfering surface characteristics, the dirty base silicate glass layer21 is subjected to a plasma treatment which involves flowing a mixtureof an oxygen-containing diamagnetic oxidant gas, such as ozone (O₃) orhydrogen peroxide (H₂ O₂) or a combination of both, and diatomic oxygen(O₂) gas into the chamber and striking an RF plasma. A mixture of 4 to15 percent O₃ or H₂ O₂ in O₂ is admitted to the chamber at a flow rateof about 2,400 standard cc/min. The plasma is sustained at a powerdensity setting of 0.25 watt/cm² to about 3.0 watt/cm² for a period offrom 30-360 seconds. In order to prevent etching of the deposited baseglass layer 21 and uncovering of additional impurity sites, aremote-source plasma generator is preferred over a parallel-platereactor. The plasma treatment is represented by FIG. 3, which depicts aplasma cloud 31 which completely engulfs the in-process integratedcircuit portion of FIG. 2, thereby exposing all surfaces of the baseglass layer 21 to the oxygen plasma. It is hypothesized that the plasmatreatment bums off impurities, such as the carbon particles, which arepresent in the PECVD-deposited base glass layer 21, thereby reducing oreliminating the hydrophilic surface characteristics. The plasmatreatment creates a high degree of surface uniformity on thePECVD-deposited base glass layer 21.

Referring once again to FIG. 2, which may also be used to represent thesecond method of forming a clean silicate glass base layer 21 involves anon-plasma-enhanced chemical vapor deposition effected by flowinghydrogen peroxide vapor and at least one gaseous compound selected fromthe group consisting of silane and disilane into the deposition chamber.A clean silicate glass base layer having no imbedded carbon particleimpurities is deposited. The reaction of hydrogen peroxide vapor witheither silane or disilane is performed within a temperature range ofabout 0° C. to 40° C., at a chamber pressure of less than about 10 torr,and at a flow rate maintained for silane or disilane within a range ofabout 10 sccm to 1,000 sccm. The hydrogen peroxide is introduced intothe deposition chamber in combination with at least one carrier gasselected from the group consisting of nitrogen and the noble gases. Thehydrogen peroxide is picked up by the carrier gas in a bubblerapparatus, and the flow rate of the carrier gas (with the hydrogenperoxide) into the deposition chamber is maintained within a range ofabout 50 sccm to 1,000 sccm. In addition, the hydrogen peroxide may beintroduced into the deposition chamber via liquid injection using aliquid-flow controller in combination with a vaporizer.

As an optional step, the clean base layer formed via this second methodmay be subjected to a plasma treatment identical to that performed onthe dirty PECVD-deposited O₂ -TEOS glass layer. This optional plasmatreatment step is performed merely to improve surface uniformity, notreduce hydrophilic surface characteristics.

Referring now to FIG. 4, an ozone-TEOS silicate glass layer 41 isdeposited on top of the clean silicate glass base layer 42. As theprocesses required for the formation of the silicate glass base layer,the plasma treatment step, and the ozone TEOS deposition step sharecertain parameters in common, the same chamber can be used for allprocess steps. For the plasma treatment step, the TEOS flow and theconcomitant carrier gas flow are terminated, plasma generationcontinues, and ozone is added to the still flowing O₂ gas. For the ozoneTEOS deposition step, the TEOS flow is resumed and the O₂ and O₃ ratiosare adjusted as necessary. The ozone TEOS deposition step isaccomplished by flowing TEOS, oxygen and ozone gases into the depositionchamber, which is maintained at a pressure greater than 10 torr, and,preferably, within a range of about 500 to 760 torr. Substratetemperatures are maintained within a range of about 300°-600° C., andpreferably at a temperature of about 400° C. A dense, highly conformalozone TEOS silicate glass layer 41 is deposited that rapidly fills inthe remaining gaps between the conductor lines 12. The ozone TEOSsilicate glass layer 41 demonstrates a high degree of conformality upondeposition. Cavities present in ozone-TEOS silicate glass layersdeposited using conventional deposition methods are eliminated.

The present process is highly advantageous because deposition of thePECVD silicate glass base layer 21, plasma treatment of the base layer21, and deposition of the ozone TEOS silicate glass layer 41 can beperformed in sequence, in the same reaction chamber, requiring a minimumof changes in the reactor, and without having to remove the substratefrom the reaction chamber between the various steps. Likewise, if thebase silicate glass layer is deposited using hydrogen peroxide andsilane or disilane as precursors, all steps may be performed within thesame reaction chamber without having to remove the substrate from thechamber between the various steps.

FIG. 5 summarizes the various options of the process which is thesubject of this disclosure. The first major step, providing a "clean"silicate glass base layer 51, can be performed in two basic ways: thedirty deposition and cleaning route 52 using TEOS and O₂ as precursorgases for a PECVD deposition step 53 followed by a cleaning plasmatreatment step 54 involving O₂ and H₂ O₂ and/or O₃, or the CVD route 55using silane or disiliane and H₂ O₂ as precursor gases in a CVDdeposition step 56 and, optionally, the plasma surface treatment of step54. The final step 57 is CVD deposition of a final glass layer usingTEOS and O₃ as precursor gases.

Various changes to the gas mixtures, temperature and pressure of thereactions are contemplated and are meant to be included herein. Althoughthe ozone-TEOS glass deposition process is described in terms of only asingle embodiment, it will be obvious to those having ordinary skill inthe art of semiconductor integrated circuit fabrication that changes andmodifications may be made thereto without departing from the scope andthe spirit of the invention as hereinafter claimed.

What is claimed is:
 1. A method for depositing silicate glass on asubstrate comprising the steps of:placing the substrate within achemical vapor deposition chamber adapted to generate a plasma forsurrounding the substrate; flowing a first gaseous mixture comprisingTEOS and diatomic oxygen into the deposition chamber while generating aplasma for surrounding the substrate in the chamber, thereby depositinga silicate glass base layer on the substrate, said base layer havingcarbonaceous impurities embedded therein, at least some of saidimpurities being exposed on an upper surface of said base layer;providing a second gaseous mixture comprising diatomic oxygen andhydrogen peroxide to form a second gaseous atmosphere; igniting a plasmain the second gaseous atmosphere; subjecting said base layer to theplasma ignited in the second gaseous atmosphere containing the mixtureof diatomic oxygen and hydrogen peroxide, thereby converting the exposedimpurities to a gas; removing the impurities converted to the gas fromcontacting said base layer; depositing a final glass layer on said uppersurface of said base layer by flowing a third gaseous atmospherecomprising TEOS gas and ozone gas into the chamber.
 2. The method ofclaim 1, wherein said second gas atmosphere is removed from the chamberprior to the deposition of the final glass layer.
 3. The method of claim1, wherein a thickness of said base layer is within a range of 100-1000Å.
 4. The method of claim 1, wherein the step of subjecting said baselayer is performed with a plasma generated with a power density settingof about 0.7 to 3.0 watts/cm².
 5. The method of claim 1, wherein thestep of subjecting said base layer to the plasma lasts for a period of30 to 360 seconds.
 6. The method of claim 1, wherein said final glasslayer is deposited at a temperature within a range of about 300° to 600°C.
 7. The method of claim 1, wherein said final glass layer is depositedat pressures within a range of about 10 to 760 torr.
 8. The method ofclaim 1, wherein said substrate is a semiconductor wafer havingincomplete integrated circuits constructed thereon.
 9. The method ofclaim 1, wherein the steps of depositing the base layer, subjecting thebase layer to a plasma, and depositing the final glass layer are allperformed in a chemical vapor deposition chamber equipped with a plasmagenerator.